1package pgs
2
3import (
4	"bufio"
5	"bytes"
6	"fmt"
7	"strings"
8	"unicode"
9	"unicode/utf8"
10)
11
12const commentPrefix = "//"
13
14// C returns a comment block, wrapping when the line's length will exceed wrap.
15func C(wrap int, args ...interface{}) string {
16	s := commentScanner(wrap, args...)
17	buf := &bytes.Buffer{}
18
19	for s.Scan() {
20		fmt.Fprintln(buf, commentPrefix, s.Text())
21	}
22
23	return buf.String()
24}
25
26// C80 is an alias for C(80, args...)
27func C80(args ...interface{}) string { return C(80, args...) }
28
29func commentScanner(wrap int, args ...interface{}) *bufio.Scanner {
30	s := bufio.NewScanner(strings.NewReader(fmt.Sprint(args...)))
31	s.Split(splitComment(wrap - 3))
32	return s
33}
34
35func splitComment(w int) bufio.SplitFunc {
36	return func(data []byte, atEOF bool) (advance int, token []byte, err error) {
37		var r rune
38
39		start := 0
40		lastSpace := 0
41
42		for width := 0; start < len(data); start += width {
43			r, width = utf8.DecodeRune(data[start:])
44			if !unicode.IsSpace(r) {
45				break
46			}
47		}
48
49		for width, i := 0, start; i < len(data); i += width {
50			r, width = utf8.DecodeRune(data[i:])
51			if unicode.IsSpace(r) {
52				if i >= w { // we are at our max comment width
53					if lastSpace == 0 { // the token cannot be broken down further, allow it to break the limit
54						return i + width, data[start:i], nil
55					}
56					return lastSpace, data[start:lastSpace], nil
57				}
58				lastSpace = i
59			}
60		}
61
62		if atEOF && len(data) > start {
63			return len(data), bytes.TrimSpace(data[start:]), nil
64		}
65
66		return start, nil, nil
67	}
68}
69